This invention relates to spring coiling machines, and more particularly, to coiling machines set up to produce relatively small springs of non-uniform diameter.
The basic construction and operating principles of spring coiling machines today closely follow those set forth in representative U.S. Pat. Nos. 2,119,002 issued May 31, 1938, for a "Spring Coiling Machine", and 2,831,570 issued Apr. 22, 1958, for "Wire Coiling Machine Having Cams for Holding The Feed Rolls Separated". In the coiling machine described in U.S. Pat. No. 2,119,002, features are described which permit the operator to adjust the initial settings and cam-controlled movement of various tools and devices that affect the characteristics of the fabricated coil springs. These characteristics can include a uniform or variable spacing between turns, and a uniform or variable turn diameter.
In such conventional machine, a round or square wire is fed through a guide block to a coiling point which plastically deforms the wire against an arbor. Typically, the wire is shaped into a continuous series of turns or loops, until the desire length of helical coil has been turned. A cut off blade is then actuated to sever a portion of the last-formed turn against the arbor. The forming diameter of the individual turns or loops in the coil is controlled by the distance between the coiling point tool and the arbor, and the size of the arbor.
Although machines of the type described above perform satisfactorily for most applications, difficulties have been encountered in setting up and operating such machines to produce small gage springs having nonuniform loop diameters. This problem arises from the conflicting requirements that an arbor having a very narrow nose is required for producing a tightly wound loop, but such a narrow arbor is somewhat delicate and susceptible to breakage as a result of the cutting blade impacting the wire against the arbor to sever the coil from the wire supply. This problem is particularly difficult in situations where the cross-sectional area of the minimum axial clearance through the coil is only about four times the cross sectional area of the wire.
An additional difficulty with conventional coil spring machines is that when forming coils with a square wire, the compressive stress imposed on the wire as it passes between the guide block and the arbor, tends to flatten the inside square edge. Although in some situations this may be desirable, in other situations, such as the fabrication of coil springs to be mounted in plastic caps to form connectors for electrical conductors, it is desirable that the wire retain a relatively sharp edge on the inside surface of the coil. Moreover, in this particular application, it is desirable that the inside edge of the coil wire not only retain a degree of sharpness, but that the inside edge also have a slight vertical tilt to increase the capability of the connector to resist pull-out of the conductors secured therein.
Conventionally, this tilt on the inside edges of the square wires for electrical connector springs, has been introduced by the pitch tool after the wire has passed the arbor. Although this technique has been marginally effective for producing the desired tilt, it has no beneficial effect on the problems mentioned above, regarding the frequent breakage of arbors due to the small sizes required to form the minimal coil diameter, and the blunting of the edges on the square wire before it reaches the pitch tool.